He had changed his name to Douglas in 1761 as heir to his uncle, but was disinherited by the Court of Session in 1767 and only confirmed in the estates by the House of Lords in 1769.
By his first wife Lady Lucy, daughter of William Graham, 2nd Duke of Montrose, he was father of the second and third Barons, the younger of whom served as MP for Lanarkshire.
By his second wife Lady Frances, daughter of Francis Scott, Earl of Dalkeith, he was father of the fourth Baron.
He had been previously elected a Scottish representative peer and this Barony gave him a permanent seat in the House of Lords.
He had married in 1832 Lucy Montagu-Scott, daughter of Henry James Montagu-Scott, 2nd Baron Montagu of Boughton by his wife Jane Margaret Douglas, daughter of the first Baron Douglas by his first wife Lucy Graham.